Answer:
17
Explanation:
We do a^2+b^2=c^2,
8^2+15^2=c^2
64+225=289
Square root of 289 = 17
c=17
You should search up Pythagorean triplets, they're basically common side lengths used for right triangles and 8,15,17 is one triplet.
Let me know if you have any questions